Dairy and similar livestock operations generate animal waste. The present invention is of particular significance in the field of dairy operations, and the invention will be described in the context of a dairy operation. The present invention may, however, have application to other environments.
In a dairy operation, cows are often held for periods of time in contained locations. Over time, cow waste collects in such contained locations and must be removed. Dairy systems thus typically use a flush system to remove cow waste from contained locations where the waste has collected. A flush system employs a pressurized liquid that is flushed onto the contained locations to remove the waste. The flush liquid and animal waste from a waste slurry that is collected and removed from the contained location.
The flush system thus requires both a continuous supply of flush liquid and a way to handle the waste slurry. To deal with both problems, processing systems have been developed that process the waste slurry generated by the flush system to obtain useable manure and, in some situations, to extract from the waste slurry a liquid suitable for use as the flush liquid.
Systems and methods of processing waste slurry generated by flush systems are described in U.S. Pat. No. 7,306,731 to DeWaard and in U.S. Patent Application Ser. No. 61/417,387, and the contents of the DeWaard '731 patent and the '387 application are incorporated herein by reference. The waste processing systems described in the DeWaard '731 patent and '387 application employ an arrangement of settling and storage tanks and liquid/solid separators to obtain useable flush liquid and also to provide a supply of material suitable for use in a digester. The flush liquid may be re-used by a conventional flush system, while the digester process yields dry solid manure material that may be safely spread directly on soil as fertilizer and/or liquid that may be used as fertilizer.
An important component of waste processing systems such as those described in the DeWaard '731 patent and the '387 application is an anaerobic digester. The process implemented by the anaerobic digester employs organisms to convert the feed material into its useable byproducts. The organisms employed by an anaerobic digester perform optimally under a narrow set of operating conditions. Further, the digesting process takes from days to weeks depending on the feed material and the conditions within the digester. The anaerobic digester can thus be a significant bottleneck in waste processing systems such as those described in the DeWaard '731 patent and the '387 application.
The present invention may be implemented as improved anaerobic digesters and, in one example implementation of the principles of the present invention, to improved waste processing systems and methods for optimizing the processing of waste slurry such as the waste slurry generated by a dairy flush system.